Russia said it will no longer export rocket engines to the U.S. to launch military satellites, adding to a dispute in Washington that already pits the two biggest U.S. defense contractors against billionaire Elon Musk.

Russian Deputy Prime Minister Dmitry Rogozin told reporters in Moscow Tuesday that Russian engines can be used only to launch civilian payloads, amid tensions over Russia’s support for separatists in Ukraine and the U.S. and European economic sanctions that followed.

The Russian-made RD-180 rocket engines are used by Centennial-based United Launch Alliance, a joint venture of top contractors Lockheed Martin Corp. and Boeing Co. that’s the sole supplier of rocket launches for the Pentagon. The engines power Atlas V rockets.

Musk’s Space Exploration Technologies Corp. has sued the U.S. Air Force, claiming it created an illegal monopoly for the military’s satellite launch business.

SpaceX also contends that the contract with ULA funnels money from American taxpayers to Russia’s military-industrial complex and potentially to those under U.S. sanctions because of the Ukraine crisis.

Last week, U.S. Federal Claims Judge Susan Braden lifted an order that temporarily blocked the Air Force from buying the Russian engines.

“ULA and our Department of Defense customers have always prepared contingency plans in the event of a supply disruption,” spokeswoman Jessica Rye said. “ULA has two launch vehicles that can support all of our customers’ needs. We also maintain a two-year inventory of engines to enable a smooth transition to our other rocket, Delta, which has all U.S.-produced rocket engines.”

Referring to Rogozin’s comments, Rye said ULA was not aware of any restrictions. But “if recent news reports are accurate, it affirms that SpaceX’s irresponsible actions have created unnecessary distractions, threatened U.S. military satellite operations, and undermined our future relationship with the International Space Station.”

Rogozin, himself a target of U.S. sanctions, also told reporters that Russia won’t extend its role in the International Space Station beyond 2020.

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